Guest

Give VOBEdit a try. Get it at http://www.doom9.org/. You may need to 'rip the DVD to your HD first. Use SmartRipper or DVDDecrytor for this.

Once the files are on the HD, you could use DVD2AVI. Simply select the first VOB of the movie and press OK to load the related files. Then select File\Save Project. The audio will be saved as a seperate .ac3 file.

I f you only want the audio from the main movie (not the extras etc) then use Movie mode in SmartRipper to save HD space.